Lesson 2: The Network Interface Card€¦ · Web viewThe Role of the Network Interface Card....

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Lesson 2: The Network Interface CardNetwork interface cards (NICs) provide the interface between cables, discussed in the previous lesson, and computers. This lesson explores the many different types of cards and how their performance affects a network. It also discusses the various connectors used to connect the cards to the cables.

After this lesson, you will be able to:

Describe the role of the NIC in a network, including preparing, sending, and controlling data.

Describe the configurable options for NICs. List the primary considerations for selecting a NIC. Describe at least two enhancements to NICs that will improve network

performance.

Estimated lesson time: 85 minutes

The Role of the Network Interface CardNetwork interface cards, usually referred to as NICs, act as the physical interface or connection between the computer and the network cable. Figure 2.24 shows a NIC with a coaxial-cable connection. The cards are installed in an expansion slot in each computer and server on the network.

After the NIC has been installed, the network cable is attached to the card's port to make the actual physical connection between the computer and the rest of the network.

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Figure 2.24 A sample NIC

The role of the NIC is to:

Prepare data from the computer for the network cable. Send the data to another computer.

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Control the flow of data between the computer and the cabling system. Receive incoming data from the cable and translate it into bytes that can

be understood by the computer's central processing unit (CPU).

Stated at a more technical level, the NIC contains the hardware and firmware (software routines stored in read-only memory, ROM) programming that implements the Logical Link Control and Media Access Control functions in the data-link layer of the OSI reference model. (See Chapter 5, Lesson 1: Open Systems Interconnection (OSI) Reference Model, for more information about the OSI reference model.)

Preparing the Data

Before data can be sent over the network, the NIC must change it from a form the computer can understand to a form that can travel over a network cable.

Data moves through a computer along paths called buses. These are actually several data paths placed side by side. Because the paths are side by side (parallel), data can move along them in lateral groups instead of in a single (serial) data stream.

Older buses, such as those used in the original IBM personal computer, were known as 8-bit buses because they could move data 8 bits at a time. The IBM PC/AT computer used a 16-bit bus, which means it could move data 16 bits at a time. Computers manufactured today use 32-bit buses. When data travels on a computer's bus, it is said to be traveling in parallel because the 32 bits are moving along side by side. Think of a 32-bit bus as a 32-lane highway with 32 cars moving side by side (moving in parallel), each carrying one bit of data.

On the network cable, however, data must travel in a single stream of bits. When data travels on a network cable it is said to be traveling as a serial transmission because one bit follows another. In other words, the cable is a one-lane highway, and the data always travels in one direction. The computer is either sending or receiving data, but never both at the same time.

The NIC takes data that is traveling in parallel as a group and restructures it so that it will flow through the 1-bit-serial path of the network cable. Figure 2.25 shows a server converting parallel data to serial data on the network. This is accomplished through the translation of the computer's digital signals into electrical or optical signals that can travel on the network's cables. The component responsible for this is the transceiver (transmitter/receiver).

Figure 2.25 Parallel data stream converted to a serial data stream

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Network Address

In addition to transforming data, the NIC also has to advertise its own location, or address, to the rest of the network to distinguish it from all the other cards on the network.

A committee of the Institute of Electrical and Electronics Engineers (IEEE) assigns blocks of addresses to each NIC manufacturer. The manufacturers hardwire these addresses into chips on the card by a process known as "burning" the address into the card. With this process, each NIC—and therefore each computer—has a unique address on a network.

The NIC also participates in several other functions in sequence as it takes data from the computer and gets it ready for the network cable:

1. The computer and NIC must communicate in order to move data from the computer to the card. On cards that can utilize direct memory access (DMA, defined later in this lesson), the computer assigns some of its memory space to the NIC.

2. The NIC signals the computer, requesting the computer's data. 3. The computer's bus moves the data from the computer's memory to the NIC.

Because data can often move faster on the bus or the cable than the NIC can handle, the data is sent to the card's buffer, a reserved portion of RAM. Here it is held temporarily during both the transmission and reception of data.

Sending and Controlling Data

Before the sending NIC actually sends data over the network, it carries on an electronic dialog with the receiving NIC so that both cards agree on the following:

The maximum size of the groups of data to be sent The amount of data to be sent before confirmation of receipt is given The time intervals between sending data chunks The amount of time to wait before confirmation is sent How much data each card can hold before it overflows The speed of the data transmission

If a newer, faster, more sophisticated NIC needs to communicate with an older, slower NIC, both need to find a common transmission speed that each can accommodate. Some newer NICs incorporate circuitry that allows the faster card to adjust to the rate of the slower card.

Each NIC signals to the other indicating its own parameters and accepting or adjusting to the other card's parameters. After all the communication details have been determined, the two cards begin to send and receive data.

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Configuration Options and SettingsNetwork interface cards often have configurable options that must be set in order for the card to function properly. Some of the older designs use externally mounted dual inline package (DIP) switches as shown in Figure 2.26. The following are examples of configurable options:

Interrupt (IRQ) Base input/output (I/O) port address Base memory address Transceiver

NOTE

Settings on older NICs are made by means of software, jumpers, or a combination of both; see the NIC product documentation for the appropriate software or jumper settings. Many newer NICs use Plug and Play (PnP) technology; consequently, older cards that require setting options manually are becoming obsolete. (Plug and Play is discussed in more detail later in this lesson.)

Figure 2.26 Older NIC with DIP switches

Interrupt Request (IRQ) Lines

Interrupt request lines (IRQs) are hardware lines over which devices such as I/O ports, the keyboard, disk drives, and NICs can send interrupts or requests for service to the computer's microprocessor.

Interrupt request lines are built into the computer's internal hardware and are assigned different levels of priority so that the microprocessor can determine the relative importance of incoming service requests.

When the NIC sends a request to the computer, it uses an interrupt—an electronic signal sent to the computer's CPU. Each device in the computer must use a different interrupt request line. The interrupt line is specified when the device is configured. For examples, see Table 2.5 that follows.

In most cases, IRQ3 or IRQ5 can be used for the NIC, as we will see later in this chapter. IRQ5 is the recommended setting if it is available, and it is the default for

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most systems. Use a system diagnostic tool to determine which IRQs are already being used.

If neither IRQ3 nor IRQ5 is available, refer to the following table for alternative values to use. The IRQs listed here as available usually can be used for a NIC. If the computer does not have the hardware device listed for a specific IRQ, that IRQ should be available for use.

Table 2.5 Standard IRQ Settings

IRQ Computer with an 80486 processor (or higher)

2(9) EGA/VGA (enhanced graphics adapter/video graphics adapter)

3 Available (unless used for second serial port [COM2, COM4] or bus mouse)

4 COM1, COM3

5 Available (unless used for second parallel port [LPT2] or sound card)

6 Floppy-disk controller

7 Parallel port (LPT1)

8 Real-time clock

10 Available

11 Available

12 Mouse (PS/2)

13 Math coprocessor

14 Hard-disk controller

15 Available (unless used for secondary hard-disk controller)

Base I/O Port

The base I/O port specifies a channel through which information flows between the computer's hardware (such as the NIC) and its CPU. The port appears to the CPU as an address.

Each hardware device in a system must have a different base I/O port number. The port numbers, in hexadecimal format (the system that uses 16 rather than 10 as the basis for its numbering) in the following table, are usually available to assign to a NIC unless they are already in use. Those with a device listed next to them are addresses commonly used for the devices. Check the computer documentation to determine which addresses are already in use.

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Table 2.6 Base I/O Port Settings

Port Device Port Device

200 to 20F

Game port

300 to 30F

NIC

210 to 21F

310 to 31F

NIC

220 to 22F

320 to 32F

Hard-disk controller (for PS/2 Model 30)

230 to 23F

Bus mouse

330 to 33F

240 to 24F

340 to 34F

250 to 25F

350 to 35F

260 to 26F

360 to 36F

270 to 27F

LPT3 370 to 37F

LPT2

280 to 28F

380 to 38F

290 to 29F

390 to 39F

2A0 to 2AF

3A0 to 3AF

2B0 to 2BF

3B0 to 3BF

LPT1

2C0 to 2CF

3C0 to 3CF

EGA/VGA

2D0 to 2DF

3D0 to 3DF

CGA/MCGA (also EGA/VGA, in color video modes)

2E0 to 2EF

3E0 to 3EF

2F0 to 2FF

COM2 3F0 to 3FF

Floppy-disk controller; COM1

Base Memory Address

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The base memory address identifies a location in a computer's memory (RAM). The NIC uses this location as a buffer area to store the incoming and outgoing data frames. This setting is sometimes called the RAM start address.

NOTE

A data frame is a packet of information transmitted as a unit on a network. Often, the base memory address for a NIC is D8000. (For some NICs, the final "0" is dropped from the base memory address—for example, D8000 would become D800.) When configuring a NIC, you must select a base memory address that is not already being used by another device. NOTE

NICs that do not use system RAM do not have a setting for the base memory address. Some NICs contain a setting that allows you to specify the amount of memory to be set aside for storing data frames. For example, for some cards you can specify either 16 KB or 32 KB of memory. Specifying more memory provides better network performance but leaves less memory available for other uses.

Selecting the Transceiver

The NIC can have other settings that need to be defined during configuration. For example, some cards come with one external and one on-board transceiver. Figure 2.27 shows a NIC with both on-board and external transceivers. In this case, you would have to decide which transceiver to use and then make the appropriate choice on your card.

Making the choice on the card is usually done with jumpers. Jumpers are small connectors that tie two pins together to determine which circuits the card will use.

Figure 2.27 Network interface card showing external and on-board transceivers

NIC, Bus, and Cable CompatibilityTo ensure compatibility between the computer and the network, the NIC must:

Fit with the computer's internal structure (data bus architecture). Have the right type of cable connector for the cabling.

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For example, a card that would work in an Apple computer communicating in a bus network will not work in an IBM computer in a ring environment: The IBM ring requires cards that are physically different from those used in a bus; and Apple uses a different network communication method.

Data Bus Architecture

In the personal computer environment, there are four types of computer bus architectures: ISA, EISA, Micro Channel, and PCI. Each type of bus is physically different from the others. It is essential that the NIC and the bus match. Figure 2.28 shows examples of each type of computer bus.

Industry Standard Architecture (ISA)

ISA is the architecture used in the IBM PC, XT, and AT computers, as well as in all their clones. It allows various adapters to be added to the system by means of plug-in cards that are inserted in expansion slots. ISA was expanded from an 8-bit path to a 16-bit path in 1984 when IBM introduced the IBM PC/AT computer. ISA refers to the expansion slot itself (an 8-bit slot or a 16-bit slot). The 8-bit slots are shorter than the 16-bit slots that actually consist of two slots, one behind the other. An 8-bit card could fit into a 16-bit slot, but a 16-bit card could not fit into an 8-bit slot.

ISA was the standard personal-computer architecture until Compaq and several other companies developed the EISA bus.

Extended Industry Standard Architecture (EISA)

This is the bus standard introduced in 1988 by a consortium of nine computer-industry companies: AST Research, Compaq, Epson, Hewlett-Packard, NEC, Olivetti, Tandy, Wyse Technology, and Zenith.

EISA offers a 32-bit data path and maintains compatibility with ISA, while providing for additional features introduced by IBM in its Micro Channel Architecture bus.

Micro Channel Architecture

IBM introduced this standard in 1988 at the time it released its PS/2 computer. Micro Channel Architecture is electrically and physically incompatible with the ISA bus. Unlike the ISA bus, the Micro Channel functions as either a 16-bit or a 32-bit bus and can be driven independently by multiple bus master processors.

Peripheral Component Interconnect (PCI)

This is a 32-bit local bus used in most Pentium computers and in the Apple Power Macintosh computers. The current PCI bus architecture meets most of the requirements for providing Plug and Play functionality. Plug and Play is both a design philosophy and a set of personal computer architecture specifications. The goal of Plug and Play is to enable changes to be made to a personal-computer configuration without any intervention by the user.

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Figure 2.28 ISA, EISA, Micro Channel, and PCI network interface cards

Network Cabling and Connectors

The network interface card performs three important functions in coordinating activities between the computer and the cabling: it

Makes the physical connection to the cable. Generates the electrical signals that travel over the cable. Controls access to the cable by following specific rules.

To select the appropriate NIC for your network, you first need to determine the type of cabling and cabling connectors it will have.

As discussed in the previous lesson, each type of cable has different physical characteristics that the NIC must accommodate. Each card is built to accept at least one type of cable. Coaxial, twisted-pair, and fiber-optic are the most common cable types.

Some NICs have more than one interface connector. For example, it is not uncommon for a NIC to have a thinnet, thicknet, and twisted-pair connector.

If a card has more than one interface connector and does not have built-in interface detection, you should make a selection by setting jumpers on the card itself or by using a software-selectable option. Consult the NIC documentation for information on how to properly configure the card. Three examples of typical connectors found on NICs are shown in the following three illustrations.

A thinnet network connection uses a coaxial BNC connector as shown in Figure 2.29.

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Figure 2.29 Thinnet network connection for a coaxial BNC connector

A thicknet network connection uses a 15-pin attachment unit interface (AUI) cable to connect the 15-pin (DB-15) connector on the back of the NIC to an external transceiver. As discussed earlier in Lesson 1, the external transceiver uses a vampire tap to connect to the thicknet cable. Figure 2.30 shows a 15-pin AUI connection.

Figure 2.30 Thicknet network connection for a 15-pin AUI

IMPORTANT

Be careful not to confuse a joystick port with an AUI external transceiver port; they look alike, but some joystick pins carry 5 volts DC, which can be harmful to network hardware as well as to the computer. You need to be familiar with the specific hardware configuration in order to determine whether the connector is for a NIC or a joystick. Similarly, be careful not to confuse 25-pin SCSI ports with parallel printer ports. Some older SCSI devices communicated through the same kind of DB-25 connector as these parallel ports, but neither device will function when plugged into the wrong connector.

An unshielded twisted-pair connection uses a RJ-45 connector, as shown in Figure 2.31. The RJ-45 connector is similar to a RJ-11 telephone connector but is larger in size and has eight conductors; a RJ-11 only has 4 conductors.

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Figure 2.31 RJ-45 connector

Network PerformanceBecause of the effect it has on data transmission, the NIC has a significant effect on the performance of the entire network. If the card is slow, data will not pass to and from the network quickly. On a bus network, where no one can use the network until the cable is clear, a slow card can increase wait times for all users.

After identifying the physical requirements of the NIC—the computer bus, the type of connector the card needs, and the type of network in which it will operate—it is necessary to consider several other factors that affect the capabilities of the card.

Although all NICs conform to certain minimum standards and specifications, some cards feature enhancements that greatly improve server, client, and overall network performance.

You can speed up the movement of data through the card by adding the following enhancements:

Direct memory access (DMA) With this method, the computer moves data directly from the NIC's buffer to the computer's memory, without using the computer's microprocessor.

Shared adapter memory In this method, the NIC contains RAM that it shares with the computer. The computer identifies this RAM as if it is actually installed in the computer.

Shared system memory In this system, the NIC's processor selects a section of the computer's memory and uses it to process data.

Bus mastering With bus mastering, the NIC takes temporary control of the computer's bus, bypasses the computer's CPU, and moves data directly to the computer's system memory. This speeds up computer operations by freeing the computer's processor to deal with other tasks. Bus mastering cards can be expensive, but they can improve network performance by 20 to 70 percent. EISA, Micro Channel, and PCI network interface cards offer bus mastering.

RAM buffering Network traffic often travels too fast for most NICs to handle. RAM chips on the NIC serve as a buffer. When the card receives more

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data than it can process immediately, the RAM buffer holds some of the data until the NIC can process it. This speeds up the card's performance and helps keep the card from becoming a bottleneck.

On-board microprocessor With a microprocessor, the NIC does not need the computer to help process data. Most cards feature their own processors that speed network operations.

Servers

Because they handle such high volumes of network traffic, servers should be equipped with the highest-performance cards possible.

Workstations

Workstations can use less expensive NICs if their main network activities are limited to applications, such as word processing, that do not generate high volumes of network traffic. Recall, though, that on a bus network, a slow NIC can increase wait times for all users. Other applications, such as those of databases or engineering, will quickly overwhelm inadequate NICs.

Specialized NICsSo far, this lesson has focused on standard network interface cards. In the majority of situations, you will be using one of these cards to connect each computer to the physical network. In reality, some situations will require the use of specialized network connections and therefore require specialized network cards. The remainder of this lesson introduces you to three varieties of these specialized cards.

Wireless NICs

Some environments require an alternative to cabled computer networking. Wireless NICs are available that support the major network operating systems. Wireless networks are discussed in detail in the next lesson.

Wireless NICs often come with many features. These include:

Indoor omnidirectional antenna and antenna cable. Network software to make the NIC work with a particular network. Diagnostic software for troubleshooting. Installation software.

These NICs can be used to create an all-wireless LAN or to add wireless stations to a cabled LAN.

Usually, these NICs are used to communicate with a component called a wireless concentrator that acts as a transceiver to send and receive signals.

NOTE

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A concentrator is a communications device that combines signals from multiple sources, such as terminals on a network, into one or more signals before sending them to their destination.

Fiber-Optic NICs

"Fiber to the desktop" has become a catchphrase for the computing industry. As transmission speeds increase to accommodate the bandwidth-hungry applications and multimedia data streams that are common on today's intranets, fiber-optic network cards allow direct connections to high-speed fiber-optic networks. These cards have recently become cost-competitive, and it's expected that their use will someday be commonplace.

Remote-Boot PROMs

In some environments, security is such an important consideration that workstations do not have individual floppy-disk drives. Without these, users are not able to copy information to floppy or hard disks and, therefore, cannot take any data from the worksite.

However, because computers normally start from either a floppy or a hard disk, there has to be another source for the software that initially starts (boots) the computer and connects it to a network. In these environments, the NIC can be equipped with a special chip called a remote-boot PROM (programmable read-only memory) that contains the hardwired code that starts the computer and connects the user to the network.

With remote-boot PROMs, diskless workstations can join the network when they start.

Lesson SummaryThe following points summarize the main elements of this lesson:

Network interface cards (NICs) are computer expansion cards that provide the interface between the network cabling and the computer.

The function of the NIC is to prepare, send, receive, and—in a Ring topology—retransmit data on the network.

A NIC is installed just like any other expansion card. You must properly set the IRQ, the base I/O port address, and the base memory address.

In order for a NIC to be physically installed in the computer and connected to the network, it must both match the computer's expansion bus type and have the proper connector fittings for the network cabling.

A network's performance is only as good as its weakest link. Many aspects of a NIC can either enhance or restrict the performance of the network. Be careful when selecting an economical card; it just might become the limiting factor in your network's performance.

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Exercise 2.2: Troubleshooting ProblemListed below are questions you need to ask regarding cabling and network interface cards when you are troubleshooting a variety of network problems. Use them to help you troubleshoot the problem that follows.

Background Information

The first troubleshooting question should always be:

Did the network connection ever function correctly in the past?

The next question should be:

What has changed since then?

Most experienced network engineers check cabling first because experience has taught them that the majority of network problems can be found in the cabling.

Is the cabling connected properly? Is the cable broken or frayed? Is the cable too long? Does the cable conform to the specifications of the NICs? Is the cable crimped or bent too sharply? Does the network cable run near a source of interference such as an air

conditioner, transformer, or large electric motor? Is the cabling terminated properly?

The most common network adapter problems are interrupt conflicts and transceiver settings. The following questions will help you determine if the NIC is the source of your problem.

Do the settings on the card match the settings in the network software you are using?

Is there an I/O address conflict between the NIC and another card installed in the computer?

Is there an interrupt conflict between the NIC and another card installed in the computer?

Is there a memory conflict between the NIC and another card installed in the computer?

Is the cable plugged into the correct interface (AUI, BNC, or RJ-45)? Is the NIC set to the speed setting that your network is using? Are you using the correct type of NIC for your network? (That is, are you

trying to use a Token Ring card in an Ethernet network?)

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If you are using more than one NIC in the computer, do their settings conflict?

The Problem

Refer back to the questions to arrive at possible causes of the situation described below. Remember that there can be more than one cause and solution.

You have a 20-user, thinnet, coaxial bus network that has been in use for about a year. Three new client computers are going to be added to the network. Your vendor installed the new computers over the weekend, but when you came in Monday morning, nobody could access the server.

1. List two things that could cause the network not to function.

NOTE

The answers identify some of the potential causes of the problem, but the list is not exhaustive. Even if the answers you have written down are not listed, they might still be correct.

2. What could you do to resolve each of the two possible causes you listed above?

3. How would each of your solutions repair the problems you identified (assuming that they are able to repair the problems)?

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Lesson 3: Wireless NetworkingThis lesson presents an overview of wireless-network technology. You are introduced to the characteristics of the various wireless environments as well as the major wireless transmission and reception components.

After this lesson, you will be able to:

Identify the three types of wireless networks and the uses of each. Describe the four transmission techniques used in local area

networking. Describe the three types of signal transmission used in mobile

computing.

Estimated lesson time: 25 minutes

The Wireless EnvironmentThe wireless environment is an often appropriate, and sometimes necessary, networking option. Today, manufacturers are offering more products at attractive prices that, in turn, will mean increased sales and demand in the future. As demand increases, the wireless environment will grow and improve.

The phrase "wireless environment" is misleading because it implies a network completely free of cabling. In most cases, this is not true. Most wireless networks actually consist of wireless components communicating with a network that uses the cabling discussed earlier in this chapter in a mixed-component network called a hybrid network.

Wireless Network Capabilities

Wireless networks are attracting attention because wireless components can:

Provide temporary connections to an existing, cabled network. Help provide backup to an existing network. Provide some degree of portability. Extend networks beyond the limits of physical connectivity.

Uses for Wireless-Network Connectivity

The inherent difficulty of setting up cable networks is a factor that will continue to push wireless environments toward greater acceptance. Wireless connectivity can be especially useful for networking:

Busy locations, such as lobbies and reception areas. Users who are constantly on the move, such as doctors and nurses in hospitals. Isolated areas and buildings.

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Departments in which the physical setting changes frequently and unpredictably.

Structures, such as historic buildings, for which cabling presents challenges.

Types of Wireless NetworksWireless networks can be divided into three categories based on their technology:

LANs Extended LANs Mobile computing

The primary difference between these categories lies in the transmission facilities. Wireless LANs and extended LANs use transmitters and receivers owned by the company in which the network operates. Mobile computing uses public carriers, such as long distance telephone companies, along with local telephone companies and their public services, to transmit and receive signals.

LANs

Except for the media used, a typical wireless network operates almost like a cabled network: a wireless network interface card with a transceiver is installed in each computer, and users communicate with the network just as if they were using cabled computers.

Access Points

The transceiver, sometimes called an access point, broadcasts and receives signals to and from the surrounding computers and passes data back and forth between the wireless computers and the cabled network.

These wireless LANs use small wall-mounted transceivers to connect to the wired network. Figure 2.32 shows a wireless connection between a laptop computer and a LAN. The transceivers establish radio contact with portable networked devices. Note that this is not a true wireless LAN, because it uses a wall-mounted transceiver to connect to a standard, cabled LAN.

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Figure 2.32 Wireless portable computer connecting to a cabled network access point

Transmission Techniques

Wireless LANs use four techniques for transmitting data:

1. Infrared transmission 2. Laser transmission 3. Narrowband (single-frequency) radio transmission 4. Spread-spectrum radio transmission

Infrared Transmission All infrared wireless networks operate by using an infrared light beam to carry the data between devices. These systems need to generate very strong signals because weak transmission signals are susceptible to interference from light sources such as windows. Many of the high-end printers sold today are preconfigured to accept infrared signals. Figure 2.33 shows a laptop computer using an infrared light beam to send data to a printer.

This method can transmit signals at high rates because of infrared light's high bandwidth. An infrared network can normally broadcast at 10 Mbps.

There are four types of infrared networks:

Line-of-sight networks As the name implies, this version of infrared networking transmits only if the transmitter and receiver have a clear line of sight between them.

Scatter infrared networks In this technology, broadcast transmissions are bounced off walls and ceilings and eventually hit the receiver. They are effective within an area limited to about 30.5 meters (100 feet).

Reflective networks Optical transceivers situated near the computers transmit to a common location that redirects the transmissions to the appropriate computer.

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Broadband optical telepoint This infrared wireless LAN provides broadband services and is capable of handling high-quality multimedia requirements that can match those provided by a cabled network.

Figure 2.33 Wireless portable computer using an infrared light beam to send data to a printer

While its speed and convenience are generating interest, infrared has difficulty transmitting for distances greater than 30.5 meters (100 feet). It is also subject to interference from the strong ambient light found in most business environments.

Laser Transmission Laser technology is similar to infrared technology in that it requires a direct line of sight, and any person or thing that breaks the laser beam will block the transmission.

Narrowband (Single-Frequency) Radio Transmission This approach is similar to broadcasting from a radio station. The user tunes both the transmitter and the receiver to a certain frequency. This does not require line-of-sight focusing because the broadcast range is 3000 meters (9842 feet). However, because the signal is high frequency, it is subject to attenuation from steel and load-bearing walls.

Narrowband radio is a subscription service. The service provider handles all the Federal Communications Commission (FCC) licensing requirements. This method is relatively slow; transmission is in the 4.8 Mbps range.

Spread-Spectrum Radio Transmission Spread-spectrum radio broadcasts signals over a range of frequencies. This helps it avoid narrowband communication problems.

The available frequencies are divided into channels, known as hops, which are comparable to one leg of a journey that includes intervening stops between the starting point and the destination. The spread-spectrum adapters tune in to a specific hop for a predetermined length of time, after which they switch to a different hop. A hopping sequence determines the timing. The computers in the network are all synchronized to the hop timing. This type of signaling provides some built-in security in that the frequency-hopping algorithm of the network would have to be known in order to tap into the data stream.

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To further enhance security and to keep unauthorized users from listening in to the broadcast, the sender and the receiver can encrypt the transmission.

Spread-spectrum radio technology provides for a truly wireless network. For example, two or more computers equipped with spread-spectrum network adapters and an operating system with built-in networking capability can act as a peer-to-peer network with no connecting cables. In addition, such a wireless network can be tied into an existing network by adding an appropriate interface to one of the computers on that network.

Although some implementations of spread-spectrum radio can offer transmission speeds of 4 Mbps over distances of about 3.22 kilometers (two miles) outdoors and 244 meters (800 feet) indoors, the typical speed of 250 Kbps (kilobits per second) makes this method much slower than the other wireless networking options discussed.

Point-to-Point Transmission

The point-to-point method of data communication does not fall neatly into the present definitions of networking. It uses a point-to-point technology that transfers data from one computer to another instead of communicating among several computers and peripherals. However, additional components such as single and host transceivers are available. These can be implemented in either stand-alone computers or computers already on a network to form a wireless data-transfer network.

This technology involves wireless serial data transfer that:

Uses a point-to-point radio link for fast, error-free data transmission. Penetrates through walls, ceilings, and floors. Supports data rates from 1.2 to 38.4 Kbps up to 61 meters (200 feet) indoors

or about 0.5 kilometers (0.30 miles) with line-of-sight transmission.

This type of system transfers data between computers, or between computers and other devices such as printers or bar-code readers.

Extended LANs

Other types of wireless components are able to function in the extended LAN environment similarly to their cabled counterparts. A wireless LAN bridge, for example, can connect networks up to 4.8 kilometers (three miles) apart.

Multipoint Wireless Connectivity

A wireless bridge is a component that offers an easy way to link buildings without using cable. In the same way that a footbridge provides a path between two points, a wireless bridge provides a data path between two buildings. Figure 2.34 shows a wireless bridge connecting two LANs. The AIRLAN/Bridge Plus, for example, uses spread-spectrum radio technology to create a wireless backbone to tie locations together over distances beyond the reach of LANs. With variations that depend on atmospheric and geographic conditions, this distance can be up to 4.8 kilometers (three miles).

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Though costly, such a component might be justified because it eliminates the expense of leased lines.

Figure 2.34 Wireless bridge connecting two LANs

The Long-Range Wireless Bridge

If the wireless bridge will not reach far enough, another alternative to consider is a long-range wireless bridge. These also use spread-spectrum radio technology to provide both Ethernet and Token Ring bridging, but for a distance of up to 40 kilometers (about 25 miles).

As with the original wireless bridge, the cost of the long-range bridge might be justified because it eliminates the need for T1 line or microwave connections.

NOTE

A T1 line is a high-speed communications line that can handle digital communications and Internet access at the rate of 1.544 Mbps.

Mobile Computing

Wireless mobile networks use telephone carriers and public services to transmit and receive signals using:

Packet-radio communication. Cellular networks. Satellite stations.

Traveling employees can use this technology with portable computers or personal digital assistants (PDAs) to exchange e-mail messages, files, or other information.

While this form of communication offers convenience, it is slow. Transmission rates range from 8 Kbps to 19.2 Kbps. The rates slow further when error correction is included.

Mobile computing incorporates wireless adapters that use cellular-telephone technology to connect portable computers with the cabled network. Portable computers use small antennas to communicate with radio towers in the surrounding

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area. Satellites in near-earth orbit pick up low-powered signals from portable and mobile networked devices.

Packet-Radio Communication

This system breaks a transmission into packets.

NOTE

A packet is a unit of information transmitted as a whole from one device to another on a network. Packets are discussed in greater detail in Chapter 3, "Understanding Network Architecture."

These radio packets are similar to other network packets. They include:

The source address. The destination address. Error-correction information.

The packets are linked up to a satellite that broadcasts them. Only devices with the correct address can receive the broadcast packets.

Cellular Networks

Cellular Digital Packet Data (CDPD) uses the same technology and some of the same systems that cellular telephones use. It offers computer data transmissions over existing analog voice networks between voice calls when the system is not busy. This is very fast technology that suffers only subsecond delays, making it reliable enough for real-time transmission.

As in other wireless networks, there must be a way to tie the cellular network in to the existing cabled network. An Ethernet interface unit (EIU) can provide this connection.

Satellite Stations

Microwave systems are a good choice for interconnecting buildings in small, short-distance systems such as those on a campus or in an industrial park.

Microwave transmission is currently the most widely used long-distance transmission method in the United States. It is excellent for communicating between two line-of-sight points such as:

Satellite-to-ground links. Between two buildings. Across large, flat, open areas, such as bodies of water or deserts.

A microwave system consists of the following:

Two radio transceivers: one to generate (transmitting station) and one to receive (receiving station) the broadcast.

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Two directional antennas pointed at each other to implement communication of the signals broadcast by the transceivers. These antennas are often installed on towers to give them more range and to raise them above anything that might block their signals.

Lesson SummaryThe following points summarize the main elements of this lesson:

The wireless environment is an often appropriate, and sometimes necessary, networking option.

Computers operating on a wireless network function like their wire-bound counterparts, except that the network interface card is connected to a transceiver instead of a cable.

A wireless segment can be either point-to-point (separated by short distances or in view of each other) or long-range.

Wireless networks use infrared, laser, narrowband radio, or spread-spectrum radio signals for transmitting data.

A wireless bridge can connect buildings that are situated as much as 40 kilometers (about 25 miles) apart.

Cellular communication, satellite stations, and packet-radio communications are adding mobility to networks.

Exercise 2.3: Network Planning ProblemThis exercise provides you with the experience of planning for two aspects of a network (selecting the right media and selecting the right NIC).

Part 1: Choosing Your Networking Media

Research has shown that about 90 percent of all new network installations are using UTP cable in a star-bus topology. Because most of the cost of cable installation is applied to labor, there is often little cost difference between using Category 3 UTP cable and Category 5 UTP cable. Most new installations use Category 5 because it supports transmission speeds of up to 100 Mbps. Category 5 allows you to install a 10 Mbps solution now and upgrade it to a 100 Mbps solution later. However, UTP cable might not be suitable for all networking situations.

The following questions prompt you to think about your network cable needs. Place a check mark next to the choice that applies to your site. To determine which type of cabling would be most appropriate for your site, simply total the check marks next to each type of cable indicator (UTP, coaxial, STP, fiber-optic). The indicator with the highest number of check marks is the candidate unless there is a specific requirement for a particular cable type such as fiber-optic (distance and security). In cases in which more than one type of cable is indicated, choose UTP where possible.

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NOTE

UTP is currently the most popular cabling option. Unless there is a compelling reason to use another type, UTP should be the first choice you consider.

For the purpose of answering the questions that follow, "Any" means that UTP can be a choice, depending on your other site considerations. "Depends on other factors" means that you will need to factor in other considerations apart from those presented in the question you're currently answering.

1. Are ease of troubleshooting and the cost of long-term maintenance important?

Yes ____ UTP cable

No ____ Any of the discussed cable types

2. Are most of your computers located within 100 meters (328 feet) of your wiring closet?

Yes ____ UTP cable

No ____ Coaxial or fiber-optic cable

3. Is ease of reconfiguration important?

Yes ____ UTP cable


4. Does any of your staff have experience with UTP cable?

Yes ____ UTP cable

No ____ UTP cable, depending on other factors (See the following Note.)

NOTE

Even if no one on your staff has experience with UTP, someone may have transferable experience with another type of cable such as coaxial, STP, or even fiber-optic cable.

5. Does your network have any existing STP cabling?

Yes ____ STP cable


6. Does the topology or NIC you want to use require the use of STP cable?

Yes ____ STP

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No ____ Depends on other factors

7. Do you have a need for cable that is more resistant than UTP to EMI (electromagnetic interference)?

Yes ____ STP, coaxial, or fiber-optic cable

No ____ UTP cable, depending on other factors

8. Do you have existing coaxial cabling in your network?

Yes ____ Coaxial cable


9. Is your network very small (10 or fewer computers)?

Yes ____ Coaxial cable (bus), UTP cable

No ____ Any of the discussed cable types, depending on other factors

10. Will your network be installed in an open area using cubicles to separate work areas?

Yes ____ Coaxial, or UTP cable

No ____ Depends on other factors

NOTE

Some situations require fiber-optic cable. This is especially true where other types of cable will not meet specific distance or security requirements. In such cases, fiber-optic cable is the only cable type that can be considered, regardless of what the questions in the other areas indicate.

11. Do you have a need for network cabling that is completely immune to electromagnetic interference (EMI)?

Yes ____ Fiber-optic cable


12. Do you have a need for network cabling that is relatively secure from most eavesdropping or corporate intelligence-gathering equipment?



13. Do you have a need for network transmission speeds that are higher than those supported by copper media?

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14. Do you have a need for longer cabling distances than those supported by copper media?



15. Do you have a budget that can absorb the costs of implementing fiber-optic cable?

Yes ____ Fiber-optic cable or any of the discussed cable types, depending on other factors


NOTE

In the questions that follow, wireless, like fiber-optic cable, may be the only option in some cases, regardless of what the questions in the other areas indicate. Keep in mind that wireless networking can also be used in combination with a cabled network.

16. Do users on your network need to physically move their computers in the course of their workday?

Yes ____ Wireless network, depends on other factors


17. Are there limitations that make it very difficult or impossible to cable computers to the network?

Yes ____ Wireless network


18. Does your network have unique needs that are best fulfilled by one or more of the features of current wireless technology, such as computer mobility, or the ability to have a network in a building in which it is very difficult or impossible to install cable?

Yes ____ Wireless network


Part 2: Choosing Your Network Interface Card

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There are dozens of manufacturers making each type of NIC, and each card has slightly different features. Setup is sometimes accomplished with jumpers or switches, sometimes using a software setup program, sometimes by means of a Plug and Play (PnP) bus type, and so on. You should do some research to determine which card is best for you because the industry is constantly changing. The best card this month might be updated or superseded by another manufacturer's card next month.

If you answer yes to each of the following questions, then the card you have chosen will probably work in your environment.

NOTE

These questions are not designed to promote a particular card but, rather, to ensure that the card you choose is compatible with the rest of your network.

1. Are drivers available for the card that can work with the operating system you are using?

Yes ____

No ____

2. Is the card compatible with the cable type and topology you have chosen?

Yes ____

No ____

3. Is the card compatible with the bus type of the computer into which it will be installed?

Yes ____

No ____

Chapter Summary

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The following points summarize the key concepts in this chapter:

Network Cabling

Three primary types of cables are used with networks: coaxial, twisted-pair, and fiber-optic.

Coaxial cable comes in two varieties: thinnet and thicknet. Thinnet cable is about 0.64 centimeters (0.25 inches) thick and can carry a

signal for a distance of up to 185 meters (607 feet). Thicknet cable is about 1.27 centimeters (0.5 inches) in diameter and can carry

a signal for a distance of up to 500 meters (1640 feet). The BNC connector is used with both thinnet and thicknet cables. Coaxial cables come in two grades, classified according to how they will be

used: PVC-grade cable is used in exposed areas; plenum-grade cable has a fire-safety rating and is used in enclosed areas such as ceilings and walls.

Twisted-pair cable can be either shielded (STP) or unshielded (UTP). The number of twists per unit of length and the protective shielding provide

protection from interference. Twisted-pair cables conform to five standards, called categories. Each

category provides specifications for increasing the speed of data transmission and resistance to interference.

Twisted-pair cables use RJ-45 connectors to connect to computers and hubs. Fiber-optic cables use light to carry digital signals. Fiber-optic cables provide the greatest protection from noise and intrusion. Data signals can be either baseband or broadband. Baseband transmission uses digital signals over a single frequency. Broadband transmission uses analog signals over a range of frequencies. IBM uses its own system of cabling and standards, but follows the same basic

technology as other cables.

The Network Interface Card

Network interface cards (NICs) are computer expansion cards that provide the interface between the network cabling and the computer.

The function of the NIC is to prepare, send, receive, and—in a Ring topology—retransmit data on the network.

A NIC is installed just like any other expansion card. You must properly set the IRQ, the base I/O port address, and the base memory address.

In order for a NIC to be physically installed in the computer and connected to the network, it must both match the computer's expansion bus type and have the proper connector fittings for the network cabling.

A network's performance is only as good as its weakest link. Many aspects of a NIC can either enhance or restrict the performance of the network. Be careful when selecting an economical card; it just might become the limiting factor in your network's performance.

Wireless Networking

The wireless environment is an often appropriate, and sometimes necessary, networking option.

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Computers operating on a wireless network function like their wire-bound counterparts, except that the NIC is connected to a transceiver instead of a cable.

A wireless segment can be either point-to-point (separated by short distances or in view of each other) or long-range.

Wireless networks use infrared, laser, narrowband radio, or spread-spectrum radio signals for transmitting data.

A wireless bridge can connect buildings that are situated as much as 40 kilometers (about 25 miles) apart.

Cellular communications, satellite stations, and packet-radio communications are adding mobility to networks.

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